The oxygen-ion conductivity of LaGaO3 electrolytes doped with BaO and MgO is studied. Curved behaviour of the oxygen ion conductivity observed in the Arrhenius plot. Therefore, the activation energy in the low-temperature region is higher than that in the high-temperature region. The dopant cation-oxygen vacancy association, especially the Mg-Ga' - V" cluster, may contribute to increase the activation energy in the low-temperature region. (C) 2001 Elsevier Science B.V. All rights reserved.